The drive control device for a vertical carrier machine is generally composed of a converter part that converts an alternating-current voltage supplied by an alternating-current primary power source into a direct-current voltage; a smoothing circuit part that smoothes the direct-current voltage converted by the converter part; an inverter that is composed of an inverter part that converts the direct-current voltage smoothed by the smoothing circuit part into an alternating-current voltage at a variable voltage variable frequency and outputs the same to an electric motor in the vertical carrier machine and the like, and an inverter control part that controls the inverter part to output an alternating-current voltage at a variable voltage variable frequency according to a velocity command, and others.
In the case where such a drive control device is used to subject the vertical elevating machine to inverter control, when the elevating machine descends or the like, the electric motor serves as a power generator to feed regenerative energy (electric power) back to the inverter side.
In the case of using a transistor inverter, a feedback diode connected in parallel to the transistor serves as a rectifier supplied power from the electric motor. Thus, since the regenerative power from the electric motor is flown into a smoothing condenser connected to a direct-current bus circuit, the voltage of the direct-current bus circuit in the inverter is increased. This brings about a problem of regeneration failure if the voltage increase is left stand. For the purpose of protecting the internal elements of the inverter, the inverter is designed such that a regeneration overvoltage detection mechanism is activated to stop operation in advance issuing an alarm.
To perform velocity control according to a decided sequence, it is necessary to control the direct-current bus circuit voltage at a predetermined constant voltage. There has been frequently used a method for processing regenerative energy by which a braking unit is installed in a direct-current main circuit, and if the direct-current bus circuit voltage increases to a specific value or more, the transistor of the braking unit is turned on under an instruction from the drive control part to flow the regenerative energy into a resistor connected in series to the transistor, and the regenerative energy is consumed as heat to prevent an increase in the direct-current bus circuit voltage.
However, according to the foregoing method, the regenerative energy is all discarded as heat, which causes a problem that electric power obtained by regenerative operation cannot be used effectively. As a system for storing and reusing regenerative energy, there is a method by which to store regenerative energy in an electric double layer capacitor provided together with a charge-discharge circuit in a single electric motor (for example, refer to Patent Document 1). According to this method, in addition to the components of a general drive system for an elevating machine in which regenerative power is consumed by a braking resistor, there are also provided a charge-discharge circuit (bidirectional DC/DC converter) connected to the direct-current bus circuit, an electric double layer capacitor that is connected to the output side of the charge-discharge circuit to store a direct-current voltage accumulated in a smoothing condenser during charging control, a voltage detection means that detects a voltage generated in the smoothing condenser, and a charge-discharge control unit that compares the detected voltage with a preset reference voltage for determination of a charge or discharge operation.